Question

Chem 4243/5243 Biochemistry homework: 1. Suppose that you discover a mutant strain of yeast whose glycolytic pathway was shorter because of the presence of a new enzyme catalyzing the reaction shown below. Would shortening the glycolytic pathway in this way benefit the cell? Explain your answer. In your answer, consider the mutant yeast growing under aerobic and anaerobic conditions. [20pts) Glyceraldehyde 3-phosphate + H+ + NAD - 3-phosphoglycerate + NADH + H

Answer 1

Usually in the Glycolysis glyceraldehyde -3-phosphate is converted to 1,3-bisphosphoglycerate by glyceraldehyde-3-phosphate dehydrogenase, with the production of one NADH, then 1,3-Bisphosphoglycerate is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase with the production of ATP.

If the mutant strain of yeast has the enzyme which converts glyceraldehyde -3-phosphate to 3-phosphoglycerate with the production of one NADH. this cell produces one ATP less during the conversion of glyceraldehyde -3-phosphate to 3-phosphoglycerate, in the glycolysis.

in glycolysis, glucose is converted to 2 molecules of Glyceraldehyde-3-phosphate, so in the pay off phase, 2 molecules of NADH and 4 molecules of ATP are produced ( ATP is also produced in the conversion of phosphoenolpyruvate to pyruvate).

In the mutant, only 2 molecules of ATP can be produced, but two molecules of ATP are used in glycolysis so the net yield of ATP via glycolysis is 0.

Yeast growing in anaerobic conditions produce energy via glycolysis, pyruvate is then converted to ethanol via alcohol fermentation.

Mutant yeast growing under anaerobic conditions cannot produce ATP, because in the mutant yeast net yield of ATP fro glycolysis is 0.

so the mutant yeast cannot grow in anaerobic conditions.

Total ATP produced from a glucose molecule via aerobic respiration is 36, for the mutant yeast growing in aerobic conditions, glucose is completely oxidized but the number of ATP produced from a glucose molecule will be 36-2=34, mutant yeast can produce 34 ATPs from a glucose molecule in aerobic conditions so the mutant yeast can grow in aerobic conditions.